Evaluation of dl ip scheduled throughput for inter enb carrier aggregation

ABSTRACT

Method, comprising determining sizes of first and second data received at PCell for transmission to UE and of secondary parts of the first and second data transmitted from PCell to SCell for transmission to UE; deciding first and second initial times of the transmission of the respective data; deciding first and second primary final times indicating an end of transmission of the respective primary parts; monitoring an indication of a throughput of SCell; obtaining a transmission delay from PCell to SCell; estimating first and second secondary final times based on transmission delay, size of the respective secondary part, and the throughput; identifying first and second latest final times among the respective primary and secondary final times; calculating first and second throughputs of the transmission of the respective data based on the size of the respective data and a respective duration between the respective initial time and latest final time.

FIELD OF THE INVENTION

The present invention relates to an apparatus, a method, and a computerprogram product related to evaluation of performance of carrieraggregation.

Abbreviations

-   3GPP 3^(rd) Generation Partnership Project-   ACK acknowledgement-   CA Carrier Aggregation-   CC Component Carrier-   DL downlink-   eNB evolved NodeB-   E-RAB Evolved RAB-   E-UTRAN Evolved UTRAN-   Gbps Gigabits per second-   gNB NodeB of NR-   HARQ hybrid automatic repeat request-   IP Internet Protocol-   LTE Long Term 3GPP Evolution-   MAC Medium Access Control-   Mbps Megabits per second-   NAS Non-access stratum-   NR New Radio-   PCell Primary Serving Cell-   PDCP Packet Data Convergence Protocol-   PDU Protocol Data Unit-   PHY Physical Layer-   PM Performance Management-   QCI QoS class identifier-   QoS Quality of Service-   RAB Radio Access Bearer-   RLC Radio Link Control-   RRC Radio Resource Control-   RTT Round trip time-   SAP Service Access Point-   SCell Secondary Serving Cell-   SDU Service Data Unit-   SI System Information-   TS Technical Specification-   TTI Transmission Time Interval-   UE User Equipment-   X2 interface between base stations (e.g. eNB, gNB)

BACKGROUND OF THE INVENTION

LTE advanced aims to support peak data rates of 1 Gbps in the downlinkand 500 Mbps in the uplink. In order to fulfill such requirements, atransmission bandwidth of up to 100 MHz is required; however, since theavailability of such large portions of contiguous spectrum is rare inpractice, LTE-Advanced uses carrier aggregation of multiple ComponentCarriers (CCs) to achieve high-bandwidth transmission. LTE-advancedsupports aggregation of up to five 20 MHz CCs.

All CCs in Release 10 are designed to be backward-compatible. This meansthat it is possible to configure each CC such that it is fullyaccessible to Release 8 User Equipments (UEs). From the higher-layerperspective, each CC appears as a separate cell with its own Cell ID. AUE that is configured for carrier aggregation connects to PrimaryServing Cell (known as the “PCell”) and up to four Secondary ServingCells (known as “SCells”). The PCell is defined as the cell that isinitially configured during connection establishment; it plays anessential role with respect to security, NAS mobility information, SIfor configured cells, and some lower layer functions.

After the initial security activation procedure, E-UTRAN may configure aUE supporting carrier aggregation with one or more SCells in addition tothe PCell that is initially configured during connection establishment.The configured set of serving cells for a UE always contains one PCelland may also contain one or more SCells. The number of serving cellsthat can be configured depends on the aggregation capability of a UE. Asingle Radio Resource Control (RRC) connection is established with thePCell, which controls all the CCs configured for a UE. Thanks to a newfunctionality, now UE is able to connect to SCells that are even fromdifferent eNBs, but still the PCell connection must remain in the eNBfrom which UE originates, where UE has established default bearerconnection. The communication between PCell and SCells in terms of IntereNB Carrier Aggregation shall take place over X2 interface.

After RRC Connection establishment to the PCell, reconfiguration,addition and removal of SCells can be performed by RRC. When adding anew SCell, dedicated RRC signaling is used to send all the required SIfor the new SCell. While in connected mode, changes of SI for an SCellare handled by release and addition of the affected SCell, and this maybe done with a single RRC reconfiguration message.

The nomenclature is as follows: Packets received by a layer (from ahigher layer) are called SDU, packets output from a layer (to a lowerlayer) are called PDU. The layers relevant in the present context arePHY-MAC-RLC-PDCP-IP in sequence from bottom to up.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the prior art.

According to a first aspect of the invention, there is provided anapparatus, comprising

-   -   means for determining configured to determine:        -   a size of a first data volume received at a primary cell and            to be transmitted to a terminal;        -   a size of a secondary part of the first data volume            transmitted on a link from the primary cell to a secondary            cell for transmission to the terminal;        -   a size of a second data volume received at the primary cell            and to be transmitted to the terminal, wherein the second            data volume is different from the first data volume;        -   a size of a secondary part of the second data volume            transmitted on the link from the primary cell to the            secondary cell for transmission to the terminal;    -   means for deciding configured to decide:        -   a first initial point in time when the transmission of the            first data volume to the terminal starts based on a start of            a transmission of a primary part of the first data volume            from the primary cell to the terminal,        -   a second initial point in time when the transmission of the            second data volume to the terminal starts based on a start            of a transmission of a primary part of the second data            volume from the primary cell to the terminal,        -   a first primary final point in time based on an end of the            transmission of the primary part of the first data volume            from the primary cell to the terminal, and        -   a second primary final point in time based on an end of the            transmission of the primary part of the second data volume            from the primary cell to the terminal;    -   means for monitoring configured to monitor if an indication of a        scheduled throughput of the secondary cell is received;    -   means for obtaining configured to obtain a link transmission        delay on the link from the primary cell to the secondary cell;    -   means for estimating configured to estimate:        -   a first secondary final point in time based on the first            initial point in time, the link transmission delay, the size            of the secondary part of the first data volume, and the            indication of the scheduled throughput, and        -   a second secondary final point in time based on the second            initial point in time, the link transmission delay, the size            of the secondary part of the second data volume, and the            indication of the scheduled throughput;    -   means for comparing configured to compare:        -   the first primary final point of time with the first            secondary final point in time to identify a first latest            final point in time among the first primary and secondary            final points in time, and        -   the second primary final point of time with the second            secondary final point in time to identify a second latest            final point in time among the second primary and secondary            final points in time;    -   means for calculating configured to calculate:        -   a first throughput of the transmission of the first data            volume to the terminal based on the size of the first data            volume and a first time duration between the first initial            point in time and the first latest final point in time, and        -   a second throughput of the transmission of the second data            volume to the terminal based on the size of the second data            volume and a second time duration between the second initial            point in time and the second latest final point in time.

For at least one of the first data volume and the second data volume,the means for calculating may be configured to calculate the respectivethroughput by dividing the size of the respective data volume by therespective time duration.

For at least one of the first data volume and the second data volume,the means for estimating may be configured to estimate the respectivesecondary final point in time by determining a respective secondarytransmission duration by dividing the size of the secondary part of therespective data volume by the scheduled throughput; and adding therespective secondary transmission duration and the link transmissiondelay to the respective initial point in time.

The means for determining may be configured to decide a respective sizeof each of one or more secondary parts of the first data volume, whereineach of the one or more secondary parts of the first data volume istransmitted on a respective link from the primary cell to a respectivesecondary cell for transmission to the terminal; the means for obtainingmay be configured to obtain a respective link transmission delay on eachof the links from the primary cell to the secondary cells; the means formonitoring may be configured to monitor if a respective indication of ascheduled throughput of each of the secondary cells is received; themeans for estimating may be configured to estimate a respective firstsecondary final point in time for each of the secondary cells, based onthe first initial point in time, the respective link transmission delay,the size of the respective secondary part of the first data volume, andthe respective indication of the scheduled throughput; the means forcomparing may be configured to compare the first primary final point oftime and the first secondary final points in time in order to identifythe first latest final point in time among the first primary andsecondary final points in time; wherein the first data volume mayconsist of the primary part of the first data volume and the one or moresecondary parts of the first data volume.

The means for determining may be configured to decide a respective sizeof each of one or more secondary parts of the second data volume,wherein each of the one or more secondary parts of the second datavolume is transmitted on a respective link from the primary cell to arespective secondary cell for transmission to the terminal; the meansfor obtaining may be configured to obtain a respective link transmissiondelay on each of the links from the primary cell to the secondary cells;the means for monitoring may be configured to monitor if a respectiveindication of a scheduled throughput of each of the secondary cells isreceived; the means for estimating may be configured to estimate arespective second secondary final point in time for each of thesecondary cells, based on the second initial point in time, therespective link transmission delay, the size of the respective secondarypart of the second data volume, and the respective indication of thescheduled throughput; the means for comparing may be configured tocompare the second primary final point of time and the second secondaryfinal points in time in order to identify the second latest final pointin time among the second primary and secondary final points in time;wherein the second data volume may consist of the primary part of thesecond data volume and the one or more secondary parts of the seconddata volume.

According to a second aspect of the invention, there is provided anapparatus comprising means for obtaining configured to obtain a measuredscheduled throughput of a scheduling of a transmission of a data volumefrom a secondary cell to a terminal, wherein the measured scheduledthroughput is related to the transmission of only the data volume, andthe data volume is received by the secondary cell from a primary cellfor the transmission to the terminal; means for providing configured toprovide an indication of an indicated scheduled throughput to theprimary cell, wherein the indicated scheduled throughput is based on themeasured scheduled throughput.

The apparatus may further comprise means for averaging configured toaverage plural measured scheduled throughputs obtained over a predefinedperiod of time in order to obtain the indicated scheduled throughput.

The indicated scheduled throughput may be equal to the measuredscheduled throughput.

According to a third aspect of the invention, there is provided amethod, comprising determining a size of a first data volume received ata primary cell and to be transmitted to a terminal; determining a sizeof a secondary part of the first data volume transmitted on a link fromthe primary cell to a secondary cell for transmission to the terminal;determining a size of a second data volume received at the primary celland to be transmitted to the terminal, wherein the second data volume isdifferent from the first data volume; determining a size of a secondarypart of the second data volume transmitted on the link from the primarycell to the secondary cell for transmission to the terminal; deciding afirst initial point in time when the transmission of the first datavolume to the terminal starts based on a start of a transmission of aprimary part of the first data volume from the primary cell to theterminal, deciding a second initial point in time when the transmissionof the second data volume to the terminal starts based on a start of atransmission of a primary part of the second data volume from theprimary cell to the terminal, deciding a first primary final point intime based on an end of the transmission of the primary part of thefirst data volume from the primary cell to the terminal, deciding asecond primary final point in time based on an end of the transmissionof the primary part of the second data volume from the primary cell tothe terminal; monitoring if an indication of a scheduled throughput ofthe secondary cell is received; obtaining a link transmission delay onthe link from the primary cell to the secondary cell; estimating a firstsecondary final point in time based on the first initial point in time,the link transmission delay, the size of the secondary part of the firstdata volume, and the indication of the scheduled throughput, estimatinga second secondary final point in time based on the second initial pointin time, the link transmission delay, the size of the secondary part ofthe second data volume, and the indication of the scheduled throughput;comparing the first primary final point of time with the first secondaryfinal point in time to identify a first latest final point in time amongthe first primary and secondary final points in time, comparing thesecond primary final point of time with the second secondary final pointin time to identify a second latest final point in time among the secondprimary and secondary final points in time; calculating a firstthroughput of the transmission of the first data volume to the terminalbased on the size of the first data volume and a first time durationbetween the first initial point in time and the first latest final pointin time, and calculating a second throughput of the transmission of thesecond data volume to the terminal based on the size of the second datavolume and a second time duration between the second initial point intime and the second latest final point in time.

According to a fourth aspect of the invention, there is provided amethod, comprising obtaining a measured scheduled throughput of ascheduling of a transmission of a data volume from a secondary cell to aterminal, wherein the measured scheduled throughput is related to thetransmission of only the data volume, and the data volume is received bythe secondary cell from a primary cell for the transmission to theterminal; providing an indication of an indicated scheduled throughputto the primary cell, wherein the indicated scheduled throughput is basedon the measured scheduled throughput.

Each of the methods of the third and fourth aspects may be a method ofdetermining throughput.

According to a fifth aspect of the invention, there is provided acomputer program product comprising a set of instructions which, whenexecuted on an apparatus, is configured to cause the apparatus to carryout the method according to any of the third and fourth aspects. Thecomputer program product may be embodied as a computer-readable mediumor directly loadable into a computer.

According to some embodiments of the invention, at least one of thefollowing advantages may be achieved:

-   -   DL IP scheduled throughput may be determined for inter-base        station carrier aggregation;    -   new measurement types are not required;    -   additional load on X2 link is very small;    -   additional load on X2 link may be adapted by adapting the        reporting interval;    -   calculation load may be on PCell or distributed between PCell        and SCell;    -   the logic of 3GPP TS 36.314 is maintained.

It is to be understood that any of the above modifications can beapplied singly or in combination to the respective aspects to which theyrefer, unless they are explicitly stated as excluding alternatives.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, features, objects, and advantages are apparent from thefollowing detailed description of the preferred embodiments of thepresent invention which is to be taken in conjunction with the appendeddrawings, wherein:

FIG. 1 shows a rejected idea of IP throughput calculation based onneighbor relation;

FIG. 2 shows a principle of a method according to some embodiments ofthe invention based on SCell's reported IP scheduled throughput;

FIG. 3 shows an example of the method according to some embodiments ofthe invention;

FIG. 4 shows an apparatus according to an embodiment of the invention;

FIG. 5 shows a method according to an embodiment of the invention;

FIG. 6 shows an apparatus according to an embodiment of the invention;

FIG. 7 shows a method according to an embodiment of the invention; and

FIG. 8 shows an apparatus according to an embodiment of the invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Herein below, certain embodiments of the present invention are describedin detail with reference to the accompanying drawings, wherein thefeatures of the embodiments can be freely combined with each otherunless otherwise described. However, it is to be expressly understoodthat the description of certain embodiments is given by way of exampleonly, and that it is by no way intended to be understood as limiting theinvention to the disclosed details.

Moreover, it is to be understood that the apparatus is configured toperform the corresponding method, although in some cases only theapparatus or only the method are described.

Currently, 3GPP (in particular 3GPP TS 36.314) does not define at allhow such Inter eNB CA Throughput should be measured.

In an implementation example of Inter eNB CA, data on PDCP layer aredivided between PCell and SCell(s). PDCP PDUs are sent over X2 interfacefrom PCell to SCell. From PDCP perspective the data transmission, whichhappens on specific cell scheduler, whether it is PCell or SCell(s), isunknown.

It is considered to measure IP Scheduled Throughput based on PDCP SDUs.An obstacle in performing such measurement is to define a way where PDCPdata volume has been properly scheduled and transmitted to the CA user,from SCell(s) perspective. As SCell scheduler is on different eNB thanPCell (for inter eNB CA), this is not a trivial task. Typically, onPCell this is currently done in such a way that each PDCP SDU is beingverified for being transmitted based on HARQ ACK confirmation from MAClayer.

One solution was proposed to create neighbour relation counters betweencells from different eNBs, and to measure over each cell the portion ofPCell data volume traffic and SCell data volume traffic, separately,done for this cell. Such solution would require a lot of counterinstances to be created (up to 12 possible relations for a given cell)and a lot of effort in implementation on lower layers. There was also anassumption that it could greatly decrease the performance of eNB andthus, the solution was rejected.

The general idea of this solution, which is based on neighbour relation,can be seen in FIG. 1, where x1 and y1 represent PCell data volume andSCell data volume, respectively, transmitted via cell 3 on eNB1.Correspondingly, x2 and y2 represent PCell data volume and SCell datavolume, respectively, transmitted via cell 1 on eNB2. So the total sumof x1, x2, y1 and y2 divided by the total time when CA data are sentfrom cell 3 on eNB1 and from cell 1 from eNB2 would directly tell usabout IP scheduled throughput obtained from certain neighbour relationbetween eNB1's cell 3 and eNB2's cell 1, driven in 3GPP TS 36.314. It isalso possible, based on this idea, to calculate CA IP scheduledthroughput from certain cell perspective, e.g. x1+y2 shall give eNB's 1cell 3 CA data volume which needs to be divided by the time when CA dataare sent for that cell.

Some embodiments of this invention provide an alternative to therejected solution.

Namely, some embodiments of the invention provide a method forevaluation of the IP scheduled throughput, according to 3GPP TS 36.314,for CA UEs handled by inter eNB(s) CA feature which is done bymeasurement of the PDCP SDU volume, by determining the size of the PDCPSDU frames transmitted to CA UEs via PCell and all the activated SCellswhich are physically located in other eNB(s), and dividing it by time ofE-RAB with data in the RLC buffer for CA UEs. In case of inter eNB(s) CAfeature the UE is considered as having data in the RLC buffer if atleast one of the involved RLC buffers, either in PCell or in at leastone of the SCells physically located in other eNB(s), is not empty,excluding last TTIs emptying the buffer. Furthermore, it is assumed thatSCell RLC buffer becomes not empty after PCell has started to transmitsome data to SCell (before that activity no data were being transmittedfrom PCell to SCell) and that SCell RLC buffer becomes empty after lastportion of the PDCP SDU (excluding last TTIs) has been successfullytransmitted to UE.

According to some embodiments of the invention, the time the data spentin RLC buffer in the SCell of eNB2 (in the following description, PCellbelongs to eNB1 and SCell belongs to eNB2) is estimated as:

$\begin{matrix}{T_{{PDCP}\mspace{11mu} {SDU}_{iBuffer}} = \frac{{PDCP}\mspace{14mu} {SDU}\mspace{14mu} {Volume}_{i}}{{IP}\mspace{14mu} {Schedule}\mspace{14mu} {Throughput}\mspace{14mu} {eNB}\; 2}} & (1)\end{matrix}$

where PDCP SDU Volume_(t) is the volume of i-th PDCP SDU frame sent fromPCell eNB1 to SCell eNB2, and IP Scheduled Throughput eNB2 as IPscheduled throughput measured according to 3GPP TS 36.314 measured ineNB2 and only for PDCP SDUs sent from eNB1 to eNB2 for inter eNB CAcase. SCell can identify these PDCP SDUs because, for inter eNB CA, aunique X2 interface is established between each PCell and SCell. PDCPSDUs arrived on this X2 interface (“relevant PDCP SDUs”) are to be takeninto account for the measurement of the IP scheduled throughput in thiscase, and other PDCP SDUs are to be disregarded for the measurement.

Note that the measurement need not be performed separately over eachburst of relevant PDCP SDUs. It may be performed over a part of a burstof relevant PDCP SDUs or over plural bursts (or parts of plural bursts)of relevant PDCP SDUs.

According to 3GPP TS 36.314, IP scheduled throughput is determined bymeasuring PDCP SDU volume transmitted to UE and dividing it by UE'stotal time with data in the RLC buffer, excluding both from numeratorand denominator the portion related to last TTIs emptying the buffer.According to some embodiments of the invention, this principle is alsokept for the inter eNB CA case. Considering parameters impacting the IPscheduled throughput it is therefore proposed according to someembodiments of the invention:

-   -   A. From the point of view of the PCell, to consider the SCell        RLC buffer physically located in eNB2 to become not-empty at the        point of time the PCell sends PDCP data to this SCell,        regardless of the point in time the data are received in RLC        layer of SCell. This proposal is driven by the fact that once        some data are sent to SCell in eNB2, the end user expects their        reception, i.e. they are acting like they would be counted in        PCell RLC buffer in intra eNB CA. In case of start of a new        burst when counting is started after first portion of data        related to this burst is sent to UE, it is assumed that firstly        PDCP data are to be considered for transmission in PCell and        after that in SCell(s), i.e. that the determination of the point        in time when a first portion of data related to this burst is        sent to UE is done in PCell (a message exchange between PCell        and SCell(s) is not needed to determine this first point in        time). This point in time can be determined as the first point        in time when data of the RLC buffer of PCell are removed.    -   B. Furthermore, it is considered that data are in the buffer        when either PCell's RLC buffer or at least one of the RLC buffer        of SCell(s) located in eNB2 has some data in it.    -   C. The time duration a given i-th PDCP SDU sent from PCell eNB        (eNB1) to SCell eNB (eNB2) is in RLC buffer, as seen from PCell        eNB1 perspective, is marked as Total_T_(PDCP SDU) _(iBuffer) .        It may be measured (determined) as follows:

Total_T _(PDCP SDU) _(iBuffer) =T _(X2_PDCP SDU) _(iBuffer) +T_(PDCP SDU) _(iBuffer)   (2)

-   -    where T_(X2_PDCP SDU) _(iBuffer) is time needed to travel from        PCell eNB (eNB1) to SCell eNB (eNB2) via X2 interface (“link        transmission delay”) and T_(PDCP SDU) _(iBuffer) is time data        related to i-th PDCP SDU spent in RLC buffer in the SCell eNB2        (excluding portion related to last TTIs) (“transmission delay”).        The latter may be measured as follows:

$\begin{matrix}{T_{{PDCP}\mspace{11mu} {SDU}_{iBuffer}} = \frac{{PDCP}\mspace{14mu} {SDU}\mspace{14mu} {Volume}_{i}}{{IP}\mspace{14mu} {Schedule}\mspace{14mu} {Throughput}\mspace{14mu} {eNB}\; 2}} & (3)\end{matrix}$

-   -    where PDCP SDU Volume_(t) is the volume (data volume) of i-th        PDCP SDU frame sent from PCell eNB1 to SCell eNB2, and IP        Scheduled Throughput eNB2 as IP scheduled throughput measured        according to 3GPP TS 36.314 measured in eNB2 and only for PDCP        SDUs sent from eNB1 to eNB2 for inter eNB CA case.    -   D. As indicated above, a massive and frequent X2 message        exchange between the PCell and SCell eNBs may not be feasible in        some cases. Therefore, in some embodiments of the invention,        equation 2 and equation 3 relay on averaged values of X2        transmission time and/or IP Scheduled Throughput eNB2. IP        Scheduled Throughput eNB2 may be communicated per a configurable        time interval (e.g. 1 minute) from eNB2 to eNB1 via X2 interface        and per the same (or another) time interval, the X2 transmission        delay may be measured, too. The X2 message exchange can be thus        decreased to 15 messages per measurement period of 15 minutes,        considering 1 minute as configured time interval.        -   For example, the X2 transmission delay can be measured as            RTT/2 related to X2 interface between eNB1 and eNB2, and RTT            may be measured by ping procedure.        -   The measurement of IP Scheduled Throughput eNB2 in eNB2            and/or the measurement of the X2 transmission delay may be            performed with the same period (time interval) as the            reporting thereof. However, in some embodiments, plural            measurements may be performed in the time interval and the            plural measurements may be averaged for the reporting to            eNB1. Also, in case of a single measurement of IP Scheduled            Throughput eNB2 per time interval, the time considered in            the measurement may be the same as the time interval, or a            shorter time duration within the time interval.

The above four points #A to #D have impact to 3GPP TS 36.314 where therelated chapter 4.1.6.1 is proposed to be modified (in bold) as shownbelow:

4.1.6.1 Scheduled IP Throughput in DL Definition Scheduled IP Throughputin DL. Throughput of PDCP SDU bits in downlink for packet sizes or databursts that are large enough to require transmissions to be split acrossseveral TTIs, by excluding transmission of the last piece of data in adata burst. Only data transmission time is considered, i.e. when datatransmission over Uu has begun but not yet finished. For UEs in intereNB Carrier Aggregation (CA) mode when PCell and SCell(s) physicallylocated in different eNBs with dedicated RLC, MAC and physical layerswhen last piece of data may occur in each of that cell all suchtransmissions shall be excluded. Also for UEs in inter eNB CA mode onlydata transmission time is considered which in this case means when datatransmission over Uu has begun but not yet finished at least in one ofthe cells physically located in other eNB . Each measurement is a realvalue representing the throughput in kbits/s. The measurement isperformed per QCI per UE. For successful reception, the reference pointis MAC upper SAP. This measurement is obtained by the following formulafor a measurement period:${{{If}\mspace{14mu} {\sum\; {ThpTimeDl}}} > 0},{\frac{\sum{ThpVolDl}}{\sum{ThpTimeDl}} \times {1000\mspace{14mu}\left\lbrack {{kbits}/s} \right\rbrack}}$If Σ ThpTimeDl = 0, 0 [kbits/s], where For small data bursts, where allbuffered data is included in one initial HARQ transmission, ThpTimeDl =0 , otherwise ThpTimeDl = T1 − T2 [ms] Explanations of the parameterscan be found in the table 4.1.6.1-1 below. Protocol Layer: PDCP, RLC,MAC

TABLE 4.1.6.1-1 ThpTimeDl The time to transmit a data burst excludingthe last piece of data transmitted in the TTI when the buffer or all thebuffers for UEs in inter eNB CA mode are emptied. A sample of“ThpTimeDl” for each time the DL buffer for one E-RAB is emptied. T1 Thepoint in time after T2 when data up until the second last piece of datain the transmitted data burst which emptied the PDCP SDU available fortransmission for the particular E-RAB was successfully transmitted, asacknowledged by the UE. T2 The point in time when the first transmissionbegins after a PDCP SDU becomes available for transmission, wherepreviously no PDCP SDUs were available for transmission for theparticular E-RAB. T1-T2 For UEs in inter eNB CA mode this timedifference shall be measured as time PDCP SDU need to travel on X2interface from PCell to SCell eNB and time data of the particular PDCPSDU spent in the buffer of SCell eNB which shall be measured as volumeof the PDCP SDU divided with IP Scheduled Throughput of SCell eNB(related to PDCP SDUs sent from PCell to SCell eNB in inter eNB CAcase). In order to avoid an overload of X2 interface the IP ScheduledThroughput of SCell eNB is recommended to be reported from SCell toPCell eNB once per a configured interval (couple of minutes). ThpVolDlThe volume of a data burst, excluding the data transmitted in the TTIwhen the buffer is emptied. For UEs in inter eNB Carrier Aggregation(CA) mode when PCell and SCell(s) physically located in different eNBswith dedicated RLC, MAC and physical layers when last piece of data mayoccur in each of that cell all such transmissions shall be excluded. Asample for ThpVolDl is the data volume, counted on PDCP SDU level, inkbits successfully transmitted (acknowledged by UE) in DL for one E- RABduring a sample of ThpTimeDl. It shall exclude the volume of the lastpiece of data emptying the buffer.

The principle of the method from implementation point of view is shownin FIG. 2. As explained in above point #B, after PCell sends data toSCell for CA, RLC layer of the SCell(s) does not inform PCell via X2interface (with the timestamp) each time the SCell RLC buffer becomesempty. Rather, SCell only informs PCell on its relevant IP scheduledthroughput. Such confirmation mechanism may be performed for each userseparately.

FIG. 3 shows an example of an embodiment of the invention with one CA UEonly and one SCell located in another eNB than the PCell. Related topoint #A above, the PCell eNB considers the SCell RLC buffer asnot-empty from the point of time the PCell sends PDCP data to this SCell(see graph #1 in FIG. 3), regardless what is the actual point in timethe data are received in RLC SCell layer (see graph #2 in FIG. 3). Onthe other hand, PCell eNB considers the SCell RLC buffer to be empty atthe point of time obtained from the timestamp using the Equation (2).Graph #3 in FIG. 3 shows when the SCell RLC Buffer from PCell/UEperspective is empty and not-empty, respectively. In relation to point#B above, PCell eNB then provides final graph #5 in FIG. 3, where thetime interval is determined when there are data in the respective bufferof any of the CA Cells. The graph #5 is obtained by an “OR function”applied to “graph #3” in FIG. 3 and “graph #4” in FIG. 3 (where graph #4in FIG. 3 shows whether or not the PCell RLC buffer is empty).

The method according to some embodiments of the invention is beneficial,because it keeps the logic of IP scheduled throughput unchanged from theend user perspective, compared with the basic definition of thismeasurement in 3GPP TS36.314. It also keeps a number of extra messagesneeded for this method on X2 interface on a low level. Even in someextreme case where such loading of X2 interface is not allowed at all,the X2 reporting for the IP Scheduled Throughput eNB2 may be completelyskipped, and as configured time interval the measurement reportinginterval (15 minutes a default) is used considering that IP ScheduledThroughput eNB2 is communicated from 3^(rd) party tools (containing PMdata from this measurement period) to PCell eNB1. Regarding thecommunication of the IP Scheduled Throughput eNB2 as an average valueper a configurable time interval (e.g. 1 minute) from eNB2 to eNB1 viaX2 interface and not per each burst follows the logic how IP scheduledthroughput is defined in 3GPP TS 36.314, which is an averagedthroughput. It is assumed that the averaging does not severely impactthe precision of the obtained throughput values.

FIG. 4 shows an apparatus according to an embodiment of the invention.The apparatus may be a base station such as a eNB or gNB or cell thereofsuch as a primary serving cell, or an element thereof. FIG. 5 shows amethod according to an embodiment of the invention. The apparatusaccording to FIG. 4 may perform the method of FIG. 5 but is not limitedto this method. The method of FIG. 5 may be performed by the apparatusof FIG. 4 but is not limited to being performed by this apparatus.

The apparatus comprises means for determining 10, means for deciding 20,means for monitoring 30, means for obtaining 40, means for estimating50, means for comparing 60, and means for calculating 70. The means fordetermining 10, means for deciding 20, means for monitoring 30, meansfor obtaining 40, means for estimating 50, means for comparing 60, andmeans for calculating 70 may be a determining means, deciding means,monitoring means, obtaining means, estimating means, comparing means,and calculating means, respectively.

The means for determining 10, means for deciding 20, means formonitoring 30, means for obtaining 40, means for estimating 50, meansfor comparing 60, and means for calculating 70 may be a determiner,decider, monitor, obtainer, estimator, comparer, and calculator,respectively. The means for determining 10, means for deciding 20, meansfor monitoring 30, means for obtaining 40, means for estimating 50,means for comparing 60, and means for calculating 70 may be adetermining processor, deciding processor, monitoring processor,obtaining processor, estimating processor, comparing processor, andcalculating processor, respectively.

The means for determining 10 determines (S10):

-   -   a size of a first data volume received at a primary cell;    -   a size of a secondary part of the first data volume;    -   a size of a second data volume received at the primary cell;    -   a size of a secondary part of the second data volume.

The first data volume and the second data volume are to be transmittedto a terminal. The second data volume is different from the first datavolume. The secondary parts of the first and second data volumes aretransmitted on a link from the primary cell (PCell) to a secondary cell(SCell) for transmission to the terminal. I.e., the primary cell and thesecondary cell may act in carrier aggregation for the terminal.

The means for deciding 20 decides a first initial point in time when thetransmission of the first data volume to the terminal starts and asecond initial point in time when the transmission of the second datavolume to the terminal starts (S20). Furthermore, the means for deciding20 decides a first primary final point in time and a second primaryfinal point in time (S25). The first and second primary final points intime are decided based on an end of the transmission of the primary partof the respective data volume from the primary cell to the terminal(i.e. directly from the PCell via an air interface to the terminal).

The sequence of S10 and S20 is arbitrary for each of the first datavolume and the second data volume. They may be performed fully or partlyin parallel.

The means for monitoring 30 monitors if an indication of a scheduledthroughput of the secondary cell is received (S30). The means forobtaining 40 obtains a link transmission delay on the link from theprimary cell to the secondary cell (S40).

The sequence of S30 and S40 is arbitrary. They may be performed fully orpartly in parallel. Also, each of S30 and S40 may be performed in anarbitrary temporal relationship to S10, S20, and S25.

The means for estimating 50 estimates first and second secondary finalpoint in time based on the respective initial point in time (decided bythe means for deciding 20), the link transmission delay (obtained by themeans for obtaining 40), the size of the secondary part of therespective data volume (determined by the means for determining 10), andthe indication of the scheduled throughput (monitored by the means formonitoring 30) (S50). At least one of the scheduled throughput and thelink transmission delay is the same for the first data volume and thesecond data volume.

For each of the first data volume and the second data volume, the meansfor comparing 60 compares the respective primary final point in timewith the respective secondary final point in time. Thus, the means forcomparing identifies respective latest final points in time among therespective primary and secondary final points in time (S60).

For each of the first data volume and the second data volume, the meansfor calculating 70 calculates a respective throughput of thetransmission of the data volume to the terminal based on a size of therespective data volume and a time duration between the respectiveinitial point in time and the respective latest final point in time(S70). In particular, the means for calculating may calculate therespective throughput as a quotient of the respective data volume andthe time duration between the respective initial point in time and therespective latest final point in time.

FIG. 6 shows an apparatus according to an embodiment of the invention.The apparatus may be a base station such as a eNB or gNB or cell thereofsuch as a secondary serving cell, or an element thereof. FIG. 7 shows amethod according to an embodiment of the invention. The apparatusaccording to FIG. 6 may perform the method of FIG. 7 but is not limitedto this method. The method of FIG. 7 may be performed by the apparatusof FIG. 6 but is not limited to being performed by this apparatus.

The apparatus comprises means for obtaining 110, and means for providing120. The means for obtaining 110, and means for providing 120 may be anobtaining means, and providing means, respectively. The means forobtaining 110, and means for providing 120 may be an obtainer, andprovider, respectively. The means for obtaining 30, and means forproviding 40 may be an obtaining processor, and providing processor,respectively.

The means for obtaining 110 obtains a measured scheduled throughput of ascheduling of a transmission of a data volume from a secondary cell to aterminal (S110). The measured scheduled throughput is related to onlythe data volume scheduled for transmission from the secondary cell tothe terminal and received by the secondary cell from a primary cell forthe transmission to the terminal.

The means for providing 120 provides an indication of an indicatedscheduled throughput to the primary cell (S120). The indicated scheduledthroughput is based on the measured scheduled throughput. For example,the indicated scheduled throughput may be the same as the measuredscheduled throughput, or the indicated scheduled throughput may be anaveraged scheduled throughput, wherein the averaging may be performedover plural measurements performed in a predefined period of time.

FIG. 8 shows an apparatus according to an embodiment of the invention.The apparatus comprises at least one processor 810, at least one memory820 including computer program code, and the at least one processor 810,with the at least one memory 820 and the computer program code, beingarranged to cause the apparatus to at least perform the method accordingto one of FIGS. 5 and 7.

In some embodiments, half of the round trip time is considered for thelink transmission delay. However, in some embodiments, other fractionsof the round trip time may be used, e.g. if the link is asymmetric suchthat transmission in one direction is faster than in the otherdirection.

In some embodiments, SCell informs PCell on its relevant IP scheduledthroughput with a fixed period. In other embodiments, SCell may informPCell on its relevant IP scheduled throughput if a certain event occurs(e.g., if a certain amount of PDCP SDUs are received over the X2interface for a CA UE or for all CA UEs of the Scell). The criteria maybe combined. E.g., SCell informs PCell after the amount of PDCP SDUs hasreceived or after the time interval has elapsed in case the receivedamount PDCP SDUs is not sufficient. If a new measurement has not beenperformed when the amount of received PDCP SDUs is sufficient, SCell mayreport the value of the previous measurement.

In some embodiments, PCell may modify the CA configuration depending onthe calculated throughput of the transmission. For example, if thecalculated throughput is lower than expected, it may select anotherSCell. As another example, if the calculated throughput is higher thanexpected, PCell may remove one or more SCells from the set of SCellsconfigured for the UE. PCell may change some radio parameters independence of the calculated throughput.

In some embodiments, PCell may estimate the duration while the PDCP SDUremain in the buffer of an SCell by a modified relationship of datavolume (at SCell) and IP scheduled throughput (at SCell). For example, afactor may take into account some packet loss on X2 interface. Anotherfactor may represent some margin because the actual IP scheduledthroughput may be different from the IP scheduled throughput indicatedby SCell. Instead of or in addition to a factor, an additive term may beadopted.

Correspondingly, in some embodiments, the calculated throughput of CAmay result from a modified relationship of (total) data volume andestimated duration. For example, the duration may be extended by sometime needed for internal processing in PCell before data for SCell aresent on X2 link and/or internal processing in SCell after arrival of thedata on X2 link. Another additive term may represent some margin for theestimation. Instead of or in addition to an additive term, a factor maybe adopted.

Some embodiments of the invention are described which are based onE-UTRAN. However, the invention is not limited to E-UTRAN and may beapplied to UTRAN or forthcoming radio access technologies such as NR. InNR, a gNB corresponds to a eNB of E-UTRAN.

The maximum number of SCells per UE is not generally limited to 4.According to some embodiments of the invention, the maximum number maybe larger or smaller than 4, or the number of SCells may be unlimited.

One piece of information may be transmitted in one or plural messagesfrom one entity to another entity. Each of these messages may comprisefurther (different) pieces of information.

Names of network elements, protocols, and methods are based on currentstandards. In other versions or other technologies, the names of thesenetwork elements and/or protocols and/or methods may be different, aslong as they provide a corresponding functionality.

If not otherwise stated or otherwise made clear from the context, thestatement that two entities are different means that they performdifferent functions. It does not necessarily mean that they are based ondifferent hardware. That is, each of the entities described in thepresent description may be based on a different hardware, or some or allof the entities may be based on the same hardware. It does notnecessarily mean that they are based on different software.

That is, each of the entities described in the present description maybe based on different software, or some or all of the entities may bebased on the same software. Each of the entities described in thepresent description may be embodied in the cloud.

According to the above description, it should thus be apparent thatexample embodiments of the present invention provide, for example, abase station (such as a gNB or eNB) or a cell (such as a primary cell ora secondary cell) thereof, or a component thereof, an apparatusembodying the same, a method for controlling and/or operating the same,and computer program(s) controlling and/or operating the same as well asmediums carrying such computer program(s) and forming computer programproduct(s).

Implementations of any of the above described blocks, apparatuses,systems, techniques or methods include, as non-limiting examples,implementations as hardware, software, firmware, special purposecircuits or logic, general purpose hardware or controller or othercomputing devices, or some combination thereof.

It is to be understood that what is described above is what is presentlyconsidered the preferred embodiments of the present invention. However,it should be noted that the description of the preferred embodiments isgiven by way of example only and that various modifications may be madewithout departing from the scope of the invention as defined by theappended claims.

1-12. (canceled)
 13. Apparatus, comprising means for determiningconfigured to determine: a size of a first data volume received at aprimary cell and to be transmitted to a terminal; a size of a secondarypart of the first data volume transmitted on a link from the primarycell to a secondary cell for transmission to the terminal; a size of asecond data volume received at the primary cell and to be transmitted tothe terminal, wherein the second data volume is different from the firstdata volume; a size of a secondary part of the second data volumetransmitted on the link from the primary cell to the secondary cell fortransmission to the terminal; means for deciding configured to decide: afirst initial point in time when the transmission of the first datavolume to the terminal starts based on a start of a transmission of aprimary part of the first data volume from the primary cell to theterminal, a second initial point in time when the transmission of thesecond data volume to the terminal starts based on a start of atransmission of a primary part of the second data volume from theprimary cell to the terminal, a first primary final point in time basedon an end of the transmission of the primary part of the first datavolume from the primary cell to the terminal, and a second primary finalpoint in time based on an end of the transmission of the primary part ofthe second data volume from the primary cell to the terminal; means formonitoring configured to monitor if an indication of a scheduledthroughput of the secondary cell is received; means for obtainingconfigured to obtain a link transmission delay on the link from theprimary cell to the secondary cell; means for estimating configured toestimate: a first secondary final point in time based on the firstinitial point in time, the link transmission delay, the size of thesecondary part of the first data volume, and the indication of thescheduled throughput, and a second secondary final point in time basedon the second initial point in time, the link transmission delay, thesize of the secondary part of the second data volume, and the indicationof the scheduled throughput; means for comparing configured to compare:the first primary final point of time with the first secondary finalpoint in time to identify a first latest final point in time among thefirst primary and secondary final points in time, and the second primaryfinal point of time with the second secondary final point in time toidentify a second latest final point in time among the second primaryand secondary final points in time; means for calculating configured tocalculate: a first throughput of the transmission of the first datavolume to the terminal based on the size of the first data volume and afirst time duration between the first initial point in time and thefirst latest final point in time, and a second throughput of thetransmission of the second data volume to the terminal based on the sizeof the second data volume and a second time duration between the secondinitial point in time and the second latest final point in time.
 14. Theapparatus according to claim 13, wherein, for at least one of the firstdata volume and the second data volume: the means for calculating isconfigured to calculate the respective throughput by dividing the sizeof the respective data volume by the respective time duration.
 15. Theapparatus according to claim 13, wherein, for at least one of the firstdata volume and the second data volume: the means for estimating isconfigured to estimate the respective secondary final point in time bydetermining a respective secondary transmission duration by dividing thesize of the secondary part of the respective data volume by thescheduled throughput; and adding the respective secondary transmissionduration and the link transmission delay to the respective initial pointin time.
 16. The apparatus according to claim 13, wherein the means fordetermining is configured to decide a respective size of each of one ormore secondary parts of the first data volume, wherein each of the oneor more secondary parts of the first data volume is transmitted on arespective link from the primary cell to a respective secondary cell fortransmission to the terminal; the means for obtaining is configured toobtain a respective link transmission delay on each of the links fromthe primary cell to the secondary cells; the means for monitoring isconfigured to monitor if a respective indication of a scheduledthroughput of each of the secondary cells is received; the means forestimating is configured to estimate a respective first secondary finalpoint in time for each of the secondary cells, based on the firstinitial point in time, the respective link transmission delay, the sizeof the respective secondary part of the first data volume, and therespective indication of the scheduled throughput; the means forcomparing is configured to compare the first primary final point of timeand the first secondary final points in time in order to identify thefirst latest final point in time among the first primary and secondaryfinal points in time; wherein the first data volume consists of theprimary part of the first data volume and the one or more secondaryparts of the first data volume.
 17. The apparatus according to claim 13,wherein the means for determining is configured to decide a respectivesize of each of one or more secondary parts of the second data volume,wherein each of the one or more secondary parts of the second datavolume is transmitted on a respective link from the primary cell to arespective secondary cell for transmission to the terminal; the meansfor obtaining is configured to obtain a respective link transmissiondelay on each of the links from the primary cell to the secondary cells;the means for monitoring is configured to monitor if a respectiveindication of a scheduled throughput of each of the secondary cells isreceived; the means for estimating is configured to estimate arespective second secondary final point in time for each of thesecondary cells, based on the second initial point in time, therespective link transmission delay, the size of the respective secondarypart of the second data volume, and the respective indication of thescheduled throughput; the means for comparing is configured to comparethe second primary final point of time and the second secondary finalpoints in time in order to identify the second latest final point intime among the second primary and secondary final points in time;wherein the second data volume consists of the primary part of thesecond data volume and the one or more secondary parts of the seconddata volume.
 18. Method, comprising determining a size of a first datavolume received at a primary cell and to be transmitted to a terminal;determining a size of a secondary part of the first data volumetransmitted on a link from the primary cell to a secondary cell fortransmission to the terminal; determining a size of a second data volumereceived at the primary cell and to be transmitted to the terminal,wherein the second data volume is different from the first data volume;determining a size of a secondary part of the second data volumetransmitted on the link from the primary cell to the secondary cell fortransmission to the terminal; deciding a first initial point in timewhen the transmission of the first data volume to the terminal startsbased on a start of a transmission of a primary part of the first datavolume from the primary cell to the terminal, deciding a second initialpoint in time when the transmission of the second data volume to theterminal starts based on a start of a transmission of a primary part ofthe second data volume from the primary cell to the terminal, deciding afirst primary final point in time based on an end of the transmission ofthe primary part of the first data volume from the primary cell to theterminal, deciding a second primary final point in time based on an endof the transmission of the primary part of the second data volume fromthe primary cell to the terminal; monitoring if an indication of ascheduled throughput of the secondary cell is received; obtaining a linktransmission delay on the link from the primary cell to the secondarycell; estimating a first secondary final point in time based on thefirst initial point in time, the link transmission delay, the size ofthe secondary part of the first data volume, and the indication of thescheduled throughput, estimating a second secondary final point in timebased on the second initial point in time, the link transmission delay,the size of the secondary part of the second data volume, and theindication of the scheduled throughput; comparing the first primaryfinal point of time with the first secondary final point in time toidentify a first latest final point in time among the first primary andsecondary final points in time, comparing the second primary final pointof time with the second secondary final point in time to identify asecond latest final point in time among the second primary and secondaryfinal points in time; calculating a first throughput of the transmissionof the first data volume to the terminal based on the size of the firstdata volume and a first time duration between the first initial point intime and the first latest final point in time, and calculating a secondthroughput of the transmission of the second data volume to the terminalbased on the size of the second data volume and a second time durationbetween the second initial point in time and the second latest finalpoint in time.
 19. The method according to claim 18, for at least one ofthe first data volume and the second data volume, further comprising:calculating the respective throughput by dividing the size of therespective data volume by the respective time duration.
 20. The methodaccording to claim 18, for at least one of the first data volume and thesecond data volume, further comprising: estimating the respectivesecondary final point in time by determining a respective secondarytransmission duration by dividing the size of the secondary part of therespective data volume by the scheduled throughput; and adding therespective secondary transmission duration and the link transmissiondelay to the respective initial point in time.
 21. The method accordingto claim 18, further comprising: deciding a respective size of each ofone or more secondary parts of the first data volume, wherein each ofthe one or more secondary parts of the first data volume is transmittedon a respective link from the primary cell to a respective secondarycell for transmission to the terminal; obtaining a respective linktransmission delay on each of the links from the primary cell to thesecondary cells; monitoring if a respective indication of a scheduledthroughput of each of the secondary cells is received; estimating arespective first secondary final point in time for each of the secondarycells, based on the first initial point in time, the respective linktransmission delay, the size of the respective secondary part of thefirst data volume, and the respective indication of the scheduledthroughput; and comparing the first primary final point of time and thefirst secondary final points in time in order to identify the firstlatest final point in time among the first primary and secondary finalpoints in time; wherein the first data volume consists of the primarypart of the first data volume and the one or more secondary parts of thefirst data volume.
 22. The method according to claim 18, furthercomprising: deciding a respective size of each of one or more secondaryparts of the second data volume, wherein each of the one or moresecondary parts of the second data volume is transmitted on a respectivelink from the primary cell to a respective secondary cell fortransmission to the terminal; obtaining a respective link transmissiondelay on each of the links from the primary cell to the secondary cells;monitoring if a respective indication of a scheduled throughput of eachof the secondary cells is received; estimating a respective secondsecondary final point in time for each of the secondary cells, based onthe second initial point in time, the respective link transmissiondelay, the size of the respective secondary part of the second datavolume, and the respective indication of the scheduled throughput; andcomparing the second primary final point of time and the secondsecondary final points in time in order to identify the second latestfinal point in time among the second primary and secondary final pointsin time; wherein the second data volume consists of the primary part ofthe second data volume and the one or more secondary parts of the seconddata volume.
 23. A computer program product comprising a set ofinstructions which, when executed on an apparatus, is configured tocause the apparatus to perform: determining a size of a first datavolume received at a primary cell and to be transmitted to a terminal;determining a size of a secondary part of the first data volumetransmitted on a link from the primary cell to a secondary cell fortransmission to the terminal; determining a size of a second data volumereceived at the primary cell and to be transmitted to the terminal,wherein the second data volume is different from the first data volume;determining a size of a secondary part of the second data volumetransmitted on the link from the primary cell to the secondary cell fortransmission to the terminal; deciding a first initial point in timewhen the transmission of the first data volume to the terminal startsbased on a start of a transmission of a primary part of the first datavolume from the primary cell to the terminal, deciding a second initialpoint in time when the transmission of the second data volume to theterminal starts based on a start of a transmission of a primary part ofthe second data volume from the primary cell to the terminal, deciding afirst primary final point in time based on an end of the transmission ofthe primary part of the first data volume from the primary cell to theterminal, deciding a second primary final point in time based on an endof the transmission of the primary part of the second data volume fromthe primary cell to the terminal; monitoring if an indication of ascheduled throughput of the secondary cell is received; obtaining a linktransmission delay on the link from the primary cell to the secondarycell; estimating a first secondary final point in time based on thefirst initial point in time, the link transmission delay, the size ofthe secondary part of the first data volume, and the indication of thescheduled throughput, estimating a second secondary final point in timebased on the second initial point in time, the link transmission delay,the size of the secondary part of the second data volume, and theindication of the scheduled throughput; comparing the first primaryfinal point of time with the first secondary final point in time toidentify a first latest final point in time among the first primary andsecondary final points in time, comparing the second primary final pointof time with the second secondary final point in time to identify asecond latest final point in time among the second primary and secondaryfinal points in time; calculating a first throughput of the transmissionof the first data volume to the terminal based on the size of the firstdata volume and a first time duration between the first initial point intime and the first latest final point in time, and calculating a secondthroughput of the transmission of the second data volume to the terminalbased on the size of the second data volume and a second time durationbetween the second initial point in time and the second latest finalpoint in time.
 24. The computer program product according to claim 23,wherein, for at least one of the first data volume and the second datavolume, the computer program product is further configured to cause theapparatus performing: calculating the respective throughput by dividingthe size of the respective data volume by the respective time duration.25. The computer program product according to claim 23, wherein, for atleast one of the first data volume and the second data volume, thecomputer program product is further configured to cause the apparatusperforming: estimating the respective secondary final point in time bydetermining a respective secondary transmission duration by dividing thesize of the secondary part of the respective data volume by thescheduled throughput; and adding the respective secondary transmissionduration and the link transmission delay to the respective initial pointin time.
 26. The computer program product according to claim 23, whereinthe computer program product is further configured to cause theapparatus performing: deciding a respective size of each of one or moresecondary parts of the first data volume, wherein each of the one ormore secondary parts of the first data volume is transmitted on arespective link from the primary cell to a respective secondary cell fortransmission to the terminal; obtaining a respective link transmissiondelay on each of the links from the primary cell to the secondary cells;monitoring if a respective indication of a scheduled throughput of eachof the secondary cells is received; estimating a respective firstsecondary final point in time for each of the secondary cells, based onthe first initial point in time, the respective link transmission delay,the size of the respective secondary part of the first data volume, andthe respective indication of the scheduled throughput; and comparing thefirst primary final point of time and the first secondary final pointsin time in order to identify the first latest final point in time amongthe first primary and secondary final points in time; wherein the firstdata volume consists of the primary part of the first data volume andthe one or more secondary parts of the first data volume.
 27. Thecomputer program product according to claim 23, wherein the computerprogram product is further configured to cause the apparatus performing:deciding a respective size of each of one or more secondary parts of thesecond data volume, wherein each of the one or more secondary parts ofthe second data volume is transmitted on a respective link from theprimary cell to a respective secondary cell for transmission to theterminal; obtaining a respective link transmission delay on each of thelinks from the primary cell to the secondary cells; monitoring if arespective indication of a scheduled throughput of each of the secondarycells is received; estimating a respective second secondary final pointin time for each of the secondary cells, based on the second initialpoint in time, the respective link transmission delay, the size of therespective secondary part of the second data volume, and the respectiveindication of the scheduled throughput; and comparing the second primaryfinal point of time and the second secondary final points in time inorder to identify the second latest final point in time among the secondprimary and secondary final points in time; wherein the second datavolume consists of the primary part of the second data volume and theone or more secondary parts of the second data volume.